Method for making polymeric structures

ABSTRACT

Polymeric structures, methods for making same, fibrous structures comprising same and fibrous product incorporating same are provided.

This application is a divisional application of U.S. application Ser.No. 10/834,504, filed Apr. 29, 2004, now U.S. Pat. No. 6,955,850,granted Oct. 18, 2005.

FIELD OF THE INVENTION

The present invention relates to polymeric structures comprising anon-PVOH processed hydroxyl polymer composition comprising a hydroxylpolymer, fibrous structures comprising such polymeric structures andmethods for making same.

BACKGROUND OF THE INVENTION

In recent years, formulators of fibrous structures have attempted tomove away from wood-based cellulosic fibers to polymeric fibers.Polymeric fiber-containing fibrous structures are known in the art. Seefor example, EP 1 217 106 A1.

However, such prior art attempts to make polymeric fiber-containingfibrous structures have failed to achieve the intensive properties oftheir wood-based cellulosic fiber-containing fibrous structure cousins.

Accordingly, there is a need for a polymeric structure and/or a fibrousstructure comprising a polymeric structure in fiber form that exhibitsintensive properties substantially similar to or better than wood-basedcellulosic fiber-containing fibrous structures.

SUMMARY OF THE INVENTION

The present invention fulfills the need described above by providing apolymeric structure and/or a fibrous structure comprising a polymericstructure in fiber form that exhibits substantially similar or betterintensive properties as compared to wood-based cellulosicfiber-containing fibrous structures.

In one aspect of the present invention, a polymeric structure comprisinga non-PVOH processed hydroxyl polymer composition comprising a hydroxylpolymer, wherein the polymeric structure exhibits a stretch at peak loadof at least about 5% and/or at least about 8% and/or at least about 10%and/or a stretch at failure load of at least about 10% and/or at leastabout 13% and/or at least about 20%, is provided.

In another aspect of the present invention, a fibrous structurecomprising a polymeric structure in the form of a fiber in accordancewith the present invention, wherein the fibrous structure exhibits astretch at peak load of at least about 5% and/or at least about 8%and/or at least about 10% and/or a stretch at failure load of at leastabout 10% and/or at least about 13% and/or at least about 20%, isprovided.

In even another aspect of the present invention, a fibrous productcomprising one or more fibrous structures in accordance with the presentinvention is provided.

In still another aspect of the present invention, a method for making apolymeric structure, the method comprising the steps of:

-   -   a. providing a non-PVOH polymer melt composition comprising a        hydroxyl polymer; and    -   b. polymer processing the non-PVOH polymer melt composition to        form a polymeric structure;    -   wherein the polymeric structure exhibits a stretch at peak load        of at least about 5% and/or at least about 8% and/or at least        about 10% and/or a stretch at failure load of at least about 10%        and/or at least about 13% and/or at least about 20%, is        provided.

In yet another aspect of the present invention, a polymeric structure infiber form produced in accordance with a method of the presentinvention, is provided.

In even still another aspect of the present invention, a method formaking a fibrous structure, the method comprising the steps of:

-   -   a. providing a non-PVOH polymer melt composition comprising a        hydroxyl polymer;    -   b. polymer processing the non-PVOH polymer melt composition to        form a polymeric structure in fiber form; and    -   c. incorporating the polymeric structure in fiber form into a        fibrous structure;    -   wherein the fibrous structure exhibits a stretch at peak load of        at least about 5% and/or at least about 8% and/or at least about        10% and/or a stretch at failure load of at least about 10%        and/or at least about 13% and/or at least about 20%, is        provided.

In even yet another aspect of the present invention, a fibrous structurecomprising two or more fibers at least one of which comprises apolymeric structure in fiber form, wherein the fibrous structurecomprises a first region comprising associated fibers and a secondregion comprising non-associated fibers, is provided.

In still yet another aspect of the present invention, a fibrous productcomprising one or more fibrous structures comprising a first regioncomprising associated fibers and a second region comprisingnon-associated fibers, is provided.

In even still yet another aspect of the present invention, a method formaking a fibrous structure, the method comprising the steps of:

-   -   a. providing a fibrous structure comprising two or more fibers        at least one of which comprises a polymeric structure in fiber        form; and    -   b. associating the two or more fibers with each other such that        a fibrous structure comprising a first region comprising        associated fibers and a second region comprising non-associated        fibers is formed, is provided.

Accordingly, the present invention provides a polymeric structure, afibrous structure comprising such a polymeric structure in fiber form, afibrous product comprising one or more such fibrous structures, methodfor making such a polymeric structure, method for making such a fibrousstructure comprising a polymeric structure in fiber form and a polymericstructure in fiber form produced by such a method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of a method for making a polymericstructure in accordance with the present invention.

FIG. 2 is a schematic illustration of a camera set-up suitable for usein the Lint/Pilling Test Method described herein.

DETAILED DESCRIPTION OF THE INVENTION Definitions

“Polymeric structure” as used herein means any physical structureproduced by polymer processing the non-PVOH polymer melt composition ofthe present invention. Nonlimiting examples of such polymeric structuresinclude fibers, films and foams. Such polymeric structures, especiallywhen in fiber form, may be used, optionally along with other physicalstructures such as cellulosic fibers and thermoplastic water-insolublepolymer fibers, to form fibrous structures. Preferably the polymericstructure of the present invention as a whole has no melting point or inother words the polymeric structure is a non-thermoplastic polymericstructure. It is also desirable that the polymeric structure of thepresent invention be substantially homogeneous.

“Non-PVOH” as used herein means that little, such as less than 5% and/orless than 3% and/or less than 1% and/or less than 0.5% by weight ofpolyvinyl alcohol is present in a composition and/or polymericstructure. In a preferred embodiment, 0% of polyvinyl alcohol is presentin a composition and/or polymeric structure.

“Fail Stretch” as used herein is defined by the following formula:

$\frac{\begin{matrix}{{{Length}\mspace{14mu}{of}\mspace{14mu}{Polymeric}\mspace{14mu}{Structure}_{FL}} -} \\{{Length}\mspace{14mu}{of}\mspace{14mu}{Polymeric}\mspace{14mu}{Structure}_{I}}\end{matrix}}{{Length}\mspace{14mu}{of}\mspace{14mu}{Polymeric}\mspace{14mu}{Structure}_{I}} \times 100\%$wherein:Length of Polymeric Structure_(FL) is the length of the polymericstructure at failure load;Length of Polymeric Structure_(I) is the initial length of the polymericstructure prior to stretching.

“Peak Stretch” as used herein is defined by the following formula:

$\frac{\begin{matrix}{{{Length}\mspace{14mu}{of}\mspace{14mu}{Polymeric}\mspace{14mu}{Structure}_{PL}} -} \\{{Length}\mspace{14mu}{of}\mspace{14mu}{Polymeric}\mspace{14mu}{Structure}_{I}}\end{matrix}}{{Length}\mspace{14mu}{of}\mspace{14mu}{Polymeric}\mspace{14mu}{Structure}_{I}} \times 100\%$wherein:Length of Polymeric Structure_(PL) is the length of the polymericstructure at peak load;Length of Polymeric Structure_(I) is the initial length of the polymericstructure prior to stretching.

The Strength of the Polymeric Structure is determined by measuring apolymeric structure's Total Dry Tensile Strength (both MD and CD) or“TDT”. TDT or Stretch is measured by providing one (1) inch by five (5)inch (2.5 cm×12.7 cm) strips of polymeric structure and/or fibrousproduct comprising such polymeric structure in need of testing. Eachstrip is placed on an electronic tensile tester Model 1122 commerciallyavailable from Instron Corp., Canton, Mass. The crosshead speed of thetensile tester is 2.0 inches per minute (about 5.1 cm/minute) and thegauge length is 1.0 inch (about 2.54 cm). The tensile tester calculatesthe stretch at Peak Load and the stretch at Failure Load. Basically, thetensile tester calculates the stretches via the formulae describedabove. The Stretch at Peak Load, as used herein, is the average of theStretch at Peak Load for MD and CD. The Stretch at Failure Load, as usedherein, is the average of the Stretch at Failure Load for MD and CD.

“Machine direction” (or MD) is the direction parallel to the flow of thepolymeric structure being made through the manufacturing equipment.

“Cross machine direction” (or CD) is the direction perpendicular to themachine direction and parallel to the general plane of the polymericstructure.

“Fiber” as used herein means a slender, thin, and highly flexible objecthaving a major axis which is very long, compared to the fiber's twomutually-orthogonal axes that are perpendicular to the major axis.Preferably, an aspect ratio of the major's axis length to an equivalentdiameter of the fiber's cross-section perpendicular to the major axis isgreater than 100/1, more specifically greater than 500/1, and still morespecifically greater than 1000/1, and even more specifically, greaterthan 5000/1.

The fibers of the present invention may be continuous or substantiallycontinuous. A fiber is continuous if it extends 100% of the MD length ofthe fibrous structure and/or fibrous product made therefrom. In oneembodiment, a fiber is substantially continuous if it extends greaterthan about 30% and/or greater than about 50% and/or greater than about70% of the MD length of the fibrous structure and/or fibrous productmade therefrom.

The fiber can have a fiber diameter as determined by the Fiber DiameterTest Method described herein of less than about 50 microns and/or lessthan about 20 microns and/or less than about 10 microns and/or less thanabout 8 microns and/or less than about 6 microns.

The polymeric structures of the present invention, especially fibers ofthe present invention, may be produced by crosslinking hydroxyl polymerstogether. In one embodiment, the polymeric structure, especially infiber form, formed as a result of the crosslinking, as a whole, exhibitsno melting point. In other words, it degrades before melting.Nonlimiting examples of a suitable crosslinking system for achievingcrosslinking comprises a crosslinking agent and optionally acrosslinking facilitator, wherein the hydroxyl polymer is crosslinked bythe crosslinking agent.

The fibers comprising a hydroxyl polymer may include melt spun fibers,dry spun fibers and/or spunbond fibers, staple fibers, hollow fibers,shaped fibers, such as multi-lobal fibers and multicomponent fibers,especially bicomponent fibers. The multicomponent fibers, especiallybicomponent fibers, may be in a side-by-side, sheath-core, segmentedpie, ribbon, islands-in-the-sea configuration, or any combinationthereof. The sheath may be continuous or non-continuous around the core.The ratio of the weight of the sheath to the core can be from about 5:95to about 95:5. The fibers of the present invention may have differentgeometries that include round, elliptical, star shaped, rectangular, andother various eccentricities.

In another embodiment, the fibers comprising a hydroxyl polymer mayinclude a multiconstituent fiber, such as a multicomponent fiber,comprising a hydroxyl polymer of the present invention along with athermoplastic, water-insoluble polymer. A multicomponent fiber, as usedherein, means a fiber having more than one separate part in spatialrelationship to one another. Multicomponent fibers include bicomponentfibers, which are defined as fibers having two separate parts in aspatial relationship to one another. The different components ofmulticomponent fibers can be arranged in substantially distinct regionsacross the cross-section of the fiber and extend continuously along thelength of the fiber.

A nonlimiting example of such a multicomponent fiber, specifically abicomponent fiber, is a bicomponent fiber in which the hydroxyl polymerrepresents the core of the fiber and the thermoplastic, water-insolublepolymer represents the sheath, which surrounds or substantiallysurrounds the core of the fiber. The polymer melt composition from whichsuch a fiber is derived preferably includes the hydroxyl polymer and thethermoplastic, water-insoluble polymer.

In another multicomponent, especially bicomponent, fiber embodiment, thesheath may comprise a hydroxyl polymer and a crosslinking system havinga crosslinking agent, and the core may comprise a hydroxyl polymer and acrosslinking system having a crosslinking agent. With respect to thesheath and core, the hydroxyl polymer may be the same or different andthe crosslinking agent may be the same or different. Further, the levelof hydroxyl polymer may be the same or different and the level ofcrosslinking agent may be the same or different.

One or more substantially continuous or continuous fibers of the presentinvention may be incorporated into a fibrous structure, such as a web.Such a fibrous structure may ultimately be incorporated into acommercial product, such as a single- or multi-ply fibrous product, suchas facial tissue, bath tissue, paper towels and/or wipes, feminine careproducts, diapers, writing papers, cores, such as tissue cores, andother types of paper products.

“Ply” or “Plies” as used herein means a single fibrous structureoptionally to be disposed in a substantially contiguous, face-to-facerelationship with other plies, forming a multi-ply fibrous product. Itis also contemplated that a single fibrous structure can effectivelyform two “plies” or multiple “plies”, for example, by being folded onitself. Ply or plies can also exist as films or other polymericstructures.

“Basis Weight” as used herein is the weight per unit area of a samplereported in lbs/3000 ft² or g/m².

Basis weight is measured by preparing one or more samples of a certainarea (m²) and weighing the sample(s) of a fibrous structure and/or filmaccording to the present invention on a top loading balance with aminimum resolution of 0.01 g. The balance is protected from air draftsand other disturbances using a draft shield. Weights are recorded whenthe readings on the balance become constant. The average weight (g) iscalculated and the average area of the samples (m²). The basis weight(g/m²) is calculated by dividing the average weight (g) by the averagearea of the samples (m²).

“Caliper” as used herein means the macroscopic thickness of a fibrousstructure, fibrous product or film. Caliper of a fibrous structure,fibrous product or film according to the present invention is determinedby cutting a sample of the fibrous structure, fibrous product or filmsuch that it is larger in size than a load foot loading surface wherethe load foot loading surface has a circular surface area of about 3.14in². The sample is confined between a horizontal flat surface and theload foot loading surface. The load foot loading surface applies aconfining pressure to the sample of 15.5 g/cm² (about 0.21 psi). Thecaliper is the resulting gap between the flat surface and the load footloading surface. Such measurements can be obtained on a VIR ElectronicThickness Tester Model II available from Thwing-Albert InstrumentCompany, Philadelphia, Pa. The caliper measurement is repeated andrecorded at least five (5) times so that an average caliper can becalculated. The result is reported in millimeters. In one embodiment ofthe present invention, the fibrous structure exhibits an average caliperthat is less than its bulk caliper

“Apparent Density” or “Density” as used herein means the basis weight ofa sample divided by the caliper with appropriate conversionsincorporated therein. Apparent density used herein has the units g/cm³.

“Weight average molecular weight” as used herein means the weightaverage molecular weight as determined using gel permeationchromatography according to the protocol found in Colloids and SurfacesA. Physico Chemical & Engineering Aspects, Vol. 162, 2000, pg. 107-121.

“Plasticity” as used herein means at least that a polymeric structureand/or fibrous structure exhibits a capability of being shaped, moldedand/or formed.

“Fibrous product” as used includes but is not limited to a wipingimplement for post-urinary and post-bowel movement cleaning (toilettissue), for otorhinolaryngological discharges (facial tissue), andmulti-functional absorbent and cleaning uses (absorbent towels).

“Lint” and/or “Pills” as used herein means discrete pieces of apolymeric structure, especially a fibrous structure and/or fibrousproduct that become separated from the original polymeric structureand/or fibrous structure and/or fibrous product typically during use.

Traditional toilet tissue and toweling are comprised essentially ofshort cellulose fibers. During the wiping process—both wet and dry,these short fibers can detach from the structure and become evident aslint or pills. The present invention employs essentially continuousfibers vs. traditional discrete, short cellulose fibers. Generallyspeaking, fibrous structures of the present invention resist linting vs.their cellulose cousins due to the continuous nature of the fibers.Furthermore, fibrous structures of the present invention will resistpilling vs. their cellulose cousins provided the bonding and fiberstrength and stretch are sufficient enough to prevent free fiberbreakage and entanglement with adjacent fibers during the wipingprocess.

“Intensive Properties” and/or “Values of Common Intensive Properties” asused herein means density, basis weight, caliper, substrate thickness,elevation, opacity, crepe frequency, and any combination thereof. Thefibrous structures of the present invention may comprise two or moreregions that exhibit different values of common intensive propertiesrelative to each other. In other words, a fibrous structure of thepresent invention may comprise one region having a first opacity valueand a second region having a second opacity value different from thefirst opacity value. Such regions may be continuous, substantiallycontinuous and/or discontinuous.

“Dry spinning” and/or “Solvent spinning” as used herein means thatpolymeric structures are not spun into a coagulating bath, unlike wetspinning.

“Associated” as used herein with respect to fibers means that two ormore discrete fibers are in close proximity to one another at one ormore positions along the fiber lengths, but less than their entirelengths such that one fiber influences the actions of the other fiber.Nonlimiting examples of means for associating fibers include bondingtogether (adhesively and/or chemically and/or electrostatically) and/orfusing together such that at the point of association one fiber unit isformed.

“Non-associated” as used herein with respect to fibers means that thefibers are not associated as defined herein.

METHODS OF THE PRESENT INVENTION

The methods of the present invention relate to producing polymericstructures such as fibers, films or foam from a non-PVOH polymer meltcomposition comprising a hydroxyl polymer and/or to producing fibrousstructures comprising a polymeric structure in fiber form.

In one nonlimiting embodiment of a method in accordance with the presentinvention, as described below, a non-PVOH polymer melt composition ispolymer processed to form a fiber. The fiber can then be incorporatedinto a fibrous structure.

Any suitable process known to those skilled in the art can be used toproduce the polymer melt composition and/or polymer process the polymermelt composition and/or the polymeric structure of the presentinvention. Nonlimiting examples of such processes are described inpublished applications: EP 1 035 239, EP 1 132 427, EP 1 217 106, EP 1217 107 and WO 03/066942.

A. Non-PVOH Polymer Melt Composition

“Non-PVOH polymer melt composition” as used herein means a compositionthat comprises a melt processed hydroxyl polymer. “Melt processedhydroxyl polymer” as used herein means any polymer, except polyvinylalcohol, that contains greater than 10% and/or greater than 20% and/orgreater than 25% by weight hydroxyl groups and that has been meltprocessed, with or without the aid of an external plasticizer and/orwith or without the presence of a pH adjusting agent. More generally,melt processed hydroxyl polymers include polymers, which by theinfluence of elevated temperatures, pressure and/or externalplasticizers may be softened to such a degree that they can be broughtinto a flowable state (all melt processing operations/processes), and inthis condition may be shaped as desired.

The non-PVOH polymer melt composition may be a composite containing ablend of different polymers, wherein at least one is a melt processedhydroxyl polymer according to the present invention, and/or fillers bothinorganic and organic, and/or fibers and/or foaming agents. In oneembodiment, the non-PVOH polymer melt composition comprises two or moredifferent melt processed hydroxyl polymers according to the presentinvention. As used herein, “different melt processed hydroxyl polymers”includes without limitation, melt processed hydroxyl polymers thatcontain at least one different moiety relative to another melt processedhydroxyl polymer and/or melt processed hydroxyl polymers that aremembers of different chemical classes (e.g., starch versus chitosan).

The non-PVOH polymer melt composition may already be formed or a meltprocessing step may need to be performed to convert a raw materialhydroxyl polymer into a melt processed hydroxyl polymer, thus producingthe non-PVOH polymer melt composition. Any suitable melt processing stepknown in the art may be used to convert the raw material hydroxylpolymer into the melt processed hydroxyl polymer.

The non-PVOH polymer melt composition may comprise a) from about 30%and/or 40% and/or 45% and/or 50% to about 75% and/or 80% and/or 85%and/or 90% and/or 99.5% by weight of the non-PVOH polymer meltcomposition of a hydroxyl polymer; b) a crosslinking system comprisingfrom about 0.1% to about 10% by weight of the non-PVOH polymer meltcomposition of a crosslinking agent; and c) from about 0% and/or 10%and/or 15% and/or 20% to about 50% and/or 55% and/or 60% and/or 70% byweight of the non-PVOH polymer melt composition of an externalplasticizer (e.g., water).

B. Polymer Processing

“Polymer processing” as used herein means any operation and/or processby which a polymeric structure comprising a processed hydroxyl polymeris formed from a non-PVOH polymer melt composition. Nonlimiting examplesof polymer processing operations include extrusion, molding and/or fiberspinning. Extrusion and molding (either casting or blown), typicallyproduce films, sheets and various profile extrusions. Molding mayinclude injection molding, blown molding and/or compression molding.Fiber spinning may include spun bonding, melt blowing, continuous fiberproducing and/or tow fiber producing.

A “processed hydroxyl polymer” as used herein means any hydroxyl polymerthat has undergone a melt processing operation and a subsequent polymerprocessing operation.

C. Polymeric Structure

The non-PVOH polymer melt composition can be subjected to one or morepolymer processing operations such that the non-PVOH polymer meltcomposition is processed into a polymeric structure such as a fiber,film or foam comprising the hydroxyl polymer and a crosslinking systemaccording to the present invention.

Post Treatment of Polymeric Structures

Once the non-PVOH polymer melt composition has been processed into apolymeric structure, such as a fiber, a film, a foam, or a plurality offibers that together form a fibrous structure, the structure may besubjected to post-treatment curing and/or differential densification.

Curing of the structure may occur before and/or after densifying aregion of the structure. Preferably curing occurs before densifying aregion of the structure.

In one embodiment, the structure produced via a polymer processingoperation may be cured at a curing temperature of from about 110° C. toabout 200° C. and/or from about 120° C. to about 195° C. and/or fromabout 130° C. to about 185° C. for a time period of from about 0.01and/or 1 and/or 5 and/or 15 seconds to about 60 minutes and/or fromabout 20 seconds to about 45 minutes and/or from about 30 seconds toabout 30 minutes prior to densifying a region of the structure.Alternative curing methods may include radiation methods such as UV,e-beam, IR and other temperature-raising methods.

Further, the structure may also be cured at room temperature for days,either after curing at above room temperature or instead of curing atabove room temperature.

The structure prior to being densified may comprise non-associatedsubstantially continuous or continuous fibers comprising a hydroxylpolymer. Further, the substantially continuous or continuous fibers maycomprise crosslinked hydroxyl polymers. Even further yet, the structuremay comprise from about 10% and/or from about 15% and/or from about 20%to about 60% and/or to about 50% and/or to about 40% by weight of thestructure of moisture.

Before differential densification, the structure may be in the form of anon-associated structure, especially if the structure comprises one ormore fibers. The structure in such non-differential densified form isinferior in intensive properties, especially tensile (stretch), than itswood-based cellulosic fibrous structure cousins.

Accordingly, the structure of the present invention may be subjected todifferential densification via a differentially densifying operation.Such differential densification can occur on-line in a continuousprocess that includes forming the structure and then differentiallydensifying the structure. Alternatively, the differential densificationcan occur off-line in a non-continuous process.

Any differentially densifying process known to those of ordinary skillin the art may be used to differentially densify the structures of thepresent invention.

As a result of differential densification, the structure comprises twoor more regions that exhibit different densities as compared to theother.

In one embodiment, the differentially densifying process comprises thestep of imparting plasticity into a structure in need of differentialdensification such that regions of different density can be created inthe structure. In other words, the differentially densifying processcomprises the step of imparting plasticity into a structure in need ofdifferential densification such that a pattern can be created in thestructure. The pattern is designed to impart regions of differentdensities in the structure. Exposing the structure in need ofdifferential densification to a humid environment, such as from about20% to about 95% and/or from about 40% to about 90% and/or from about50% to about 85% and/or from about 65% to about 80% relative humidityfor a sufficient time, such as at least 1 second and/or at least 3seconds and/or at least 5 seconds, can impart sufficient plasticity tothe structure to permit differential densification to be created in thestructure.

In one embodiment, the differentially densifying process comprisessubjecting the structure to a patterned roller such that the pattern onthe roller is imparted to the structure, thus causing the structure tobecome differentially densified.

In another embodiment, the differentially densifying process comprisescontacting the structure, which is in contact with a patternedbelt/fabric with pressure from a smooth roller thus imparting thepattern of the belt/fabric to the structure causing the structure tobecome differentially densified.

The differentially densifying of a structure in accordance with thepresent invention preferably occurs after the structure has been formed,not concurrent with the formation of the structure.

The structure of the present invention may be differentially densifiedmore than once. For example, a structure may be differentiallydensified, then cured, and then differentially densified again accordingto the present invention.

In another embodiment, the structure may comprise two or more “plies” ofstructure which can then be differentially densified as a multi-plystructure.

The structure may be differentially densified, then differentialdensified again and then cured.

Alternatively, the structure of the present invention may be cured, thendifferentially densified according to the present invention

Curing of the structure, in accordance with the present invention, mayoccur at any point in time relative to any differentially densifyingprocess. It may occur before (preferably immediately before), after(preferably immediately after), before and after (preferably immediatelybefore and immediately after), or not at all.

The differentially densifying process may occur once or a plurality oftimes.

Ultrasonics may also be used to aid in differential densification of thestructure, especially in conjunction with a patterned roller. Theultrasonics may be generated by any suitable ultrasonic device. Forexample, a horn or ultrasonic wave generator that is capable ofimparting energy to the structure such that the structure deformsaccording to the pattern on the patterned roller can be used.

In still another embodiment, the step of differentially densifyingcomprises contacting the fibrous structure with a structure-impartingelement comprising a pattern in the presence of humidity and applying aforce to the fibrous structure and/or structure-imparting element suchthat the fibrous structure takes the shape of the pattern on thestructure-imparting element to form a differential densified polymericstructure.

In yet still another embodiment, step of differentially densifying thefibrous structure comprises sandwiching the fibrous structure betweentwo belts in the presence of humidity, wherein at least one of the beltsis a structured belt comprising a pattern and applying a force to atleast one of the belts such that the fibrous structure takes the shapeof the pattern on the structured belt to form a differential densifiedpolymeric structure.

A nonlimiting example of a differential densification process fordifferentially densifying a structure in accordance with the presentinvention is provided below.

Differential Densification Example

A non-PVOH polymer melt composition containing approximately 40% wateris extruded from a twin screw extruder. Crosslinker and other additivesare introduced into the melt and mixed via in-line static mixers. Thenon-PVOH polymer melt composition with additives is then pumped to ameltblown style spinnerette where fibers are extruded and attenuatedinto fine fibers. One suitable hydroxyl polymer is starch under thetradename Penfilm 162, available from Penford Products Inc. Crosslinkersand additives used are urea glyoxal adduct (“UGA”), ammonium sulfate,and acrylic latex. Total additives are typically 10% or less on a wt %basis of dry hydroxyl polymer. The attenuated fibers are dried withentrained hot air and deposited on a collector belt. The collector beltis typically set at 22-25″ from the end of the spinnerette and thestructure, a fibrous structure, formed on the collector belts is anon-associated fibrous structure.

FIG. 1 schematically illustrates one embodiment of a differentialdensification operation 10. After forming, the non-associated fibrousstructure 12 is subjected to an environmentally controlled humidenvironment, such as in a humidity chamber 14. Typical relative humidityrange is 70-78%. As the fibrous structure 12 is conveyed through thechamber 14, the fine starch fibers are plasticized, allowingdifferential densification to be possible. Upon exiting the chamber 14,the plasticized fibrous structure 12′ is passed through a patterned nip16 to associate regions of the fibrous structure, thus producing anassociated fibrous structure 12″. The associated fibrous structureregions 18 correspond to the pattern utilized on either the carrier belt(not shown) or the roller itself 20. One patterned belt employed hasbeen a square weave open mesh belt, available from Albany InternationalInc and known as style “Filtratech 10”. Nip pressure varies depending onthe pattern employed, but is typically in the 200-300 pli range. Thefibers present in the fibrous structure are now associated and thefibrous structure exhibits excellent handling properties. After a curingperiod for the crosslinking system and additives to react, theassociated fibrous structure exhibits dry and wet properties acceptablefor disposable fibrous products and can be used as a variety ofdisposable implements, especially toilet tissue or toweling. The tablebelow summarizes key physical properties of one embodiment of a fibrousstructure in accordance with the present invention at differentconditions; namely, pre-differential densification, post-differentialdensification, and post-differential densification cured as compared toa typical commercial tissue such as Charmin® 1-ply.

Typical Post Tissue Pre- Post densification (Charmin ® densificationdensification Cured 1-ply) Dry MD + CD 142 293 441 400 Tensile g/in DryFail 29 16 18 25 Stretch % Dry Burst g 80 92 261 150 Dry Burst 0.5 0.471.5 1.7 Energy g/cm Basis Weight 36 36 36 36 g/m²Hydroxyl Polymers

Hydroxyl polymers in accordance with the present invention include anyhydroxyl-containing polymer, with the exception of polyvinyl alcohol,that can be incorporated into a polymeric structure of the presentinvention, preferably in the form of a fiber.

In one embodiment, the hydroxyl polymer of the present inventionincludes greater than 10% and/or greater than 20% and/or greater than25% by weight hydroxyl moieties.

Nonlimiting examples of hydroxyl polymers in accordance with the presentinvention include polyols, such as starch, starch derivatives, chitosan,chitosan derivatives, cellulose derivatives such as cellulose ether andester derivatives, gums, arabinans, galactans, proteins and variousother polysaccharides and mixtures thereof.

The hydroxyl polymer preferably has a weight average molecular weight offrom about 10,000 to about 40,000,000 g/mol. Higher and lower molecularweight hydroxyl polymers may be used in combination with hydroxylpolymers having the preferred weight average molecular weight.

Well known modifications of natural starches include chemicalmodifications and/or enzymatic modifications. For example, the naturalstarch can be acid-thinned, hydroxy-ethylated or hydroxy-propylated oroxidized.

“Polysaccharides” herein means natural polysaccharides andpolysaccharide derivatives or modified polysaccharides. Suitablepolysaccharides include, but are not limited to, gums, arabinans,galactans and mixtures thereof.

Crosslinking System

The crosslinking system of the present invention may further comprise,in addition to the crosslinking agent, a crosslinking facilitator.

“Crosslinking facilitator” as used herein means any material that iscapable of activating a crosslinking agent thereby transforming thecrosslinking agent from its unactivated state to its activated state. Inother words, when a crosslinking agent is in its unactivated state, thehydroxyl polymer present in the non-PVOH polymer melt composition doesnot undergo premature crosslinking (“unacceptable” crosslinking) asdetermined according to the Shear Viscosity Change Test Method describedherein.

When a crosslinking agent in accordance with the present invention is inits activated state, the hydroxyl polymer present in the polymericstructure may, and preferably does, undergo acceptable crosslinking viathe crosslinking agent as determined according to the Initial Total WetTensile Test Method described herein.

The crosslinking facilitator may include derivatives of the materialthat may exist after the transformation/activation of the crosslinkingagent. For example, a crosslinking facilitator salt being chemicallychanged to its acid form and vice versa.

A crosslinking system may be present in the non-PVOH polymer meltcomposition and/or may be added to the non-PVOH polymer melt compositionbefore polymer processing of the non-PVOH polymer melt composition.

Nonlimiting examples of suitable crosslinking facilitators include acidshaving a pKa of between about 0 and about 6 and/or between about 1.5 andabout 6 and/or between about 2 and about 6 or salts thereof. Thecrosslinking facilitators may be Bronsted Acids and/or salts thereof,preferably ammonium salts thereof.

In addition, metal salts, such as magnesium and zinc salts, can be usedalone or in combination with Bronsted Acids and/or salts thereof, ascrosslinking facilitators.

Nonlimiting examples of suitable crosslinking facilitators includeacetic acid, benzoic acid, citric acid, formic acid, glycolic acid,lactic acid, maleic acid, phthalic acid, phosphoric acid, sulfuric acid,succinic acid and mixtures thereof ad/or their salts, preferably theirammonium salts, such as ammonium glycolate, ammonium citrate andammonium sulfate.

Nonlimiting examples of suitable crosslinking agents includepolycarboxylic acids, imidazolidinones and other compounds resultingfrom alkyl substituted or unsubstituted cyclic adducts of glyoxal withureas, thioureas, guanidines, methylene diamides, and methylenedicarbamates and derivatives thereof; and mixtures thereof.

Test Methods

All tests described herein including those described under theDefinitions section and the following test methods are conducted onsamples that have been conditioned in a conditioned room at atemperature of 73° F.±4° F. (about 23° C.±2.2° C.) and a relativehumidity of 50%±10% for 24 hours prior to the test. Further, all testsare conducted in such conditioned room. Tested samples and felts shouldbe subjected to 73° F.±4° F. (about 23° C.±2.2° C.) and a relativehumidity of 50%±10% for 24 hours prior to capturing images.

A. Lint/Pilling Test Method

i. Sample Preparation

Prior to the testing, fibrous product samples, 4.5″×16″ strips offibrous product, are conditioned according to Tappi Method #T402OM-88.

Each fibrous product sample (6 samples if testing both sides, 3 samplesif testing a single side) is first prepared by removing and discardingany pieces of the sample which might have been abraded in handling. Forfibrous products formed from multiple plies of fibrous structure, thistest can be used to make a lint measurement on the multi-ply fibrousproduct, or, if the plies can be separated without damaging the fibrousproduct, a measurement can be taken on the individual plies making upthe fibrous product. If a given sample differs from surface to surface,it is necessary to test both surfaces and average the scores in order toarrive at a composite lint score. In some cases, fibrous products aremade from multiple-plies of fibrous structures such that the facing-outsurfaces are identical, in which case it is only necessary to test onesurface.

Each sample is folded upon itself to make a 4.5″ CD×4″ MD sample. Fortwo-surface testing, make up 3 (4.5″ CD×4″ MD) samples with a firstsurface “out” and 3 (4.5″ CD×4″ MD) samples with the second surface“out”. Keep track of which samples are first surface “out” and which aresecond surface “out”.

Obtain a 30″×40″ piece of Crescent #300 cardboard from Cordage Inc. (800E. Ross Road, Cincinnati, Ohio, 45217). Using a paper cutter, cut outsix pieces of cardboard of dimensions of 2.5″×6″. Puncture two holesinto each of the six pieces of cardboard by forcing the cardboard ontothe hold down pins of the Sutherland Rub tester.

Center and carefully place each of the cardboard pieces on top of thesix (two surface testing) or three (single surface testing) previouslyfolded samples. Make sure the 6″ dimension of the cardboard is runningparallel to the machine direction (MD) of each of the samples.

Fold one edge of the exposed portion of the sample onto the back of thecardboard. Secure this edge to the cardboard with adhesive tape obtainedfrom 3M Inc. (¾″ wide Scotch Brand, St. Paul, Minn.). Carefully graspthe other over-hanging tissue edge and snugly fold it over onto the backof the cardboard. While maintaining a snug fit of the sample onto thecardboard, tape this second edge to the back of the cardboard. Repeatthis procedure for each sample.

Turn over each sample and tape the cross direction edges of the sampleto the cardboard for the dry lint/pilling test. One half of the adhesivetape should contact the sample while the other half is adhering to thecardboard. Repeat this procedure for each of the samples. If the samplebreaks, tears, or becomes frayed at any time during the course of thissample preparation procedure, discard and make up a new sample with asample strip.

For the wet lint/pilling test, tape the leading cross direction edge ofthe sample to the cardboard and a table top upon which the sample isplaced. Position the sample on the cardboard such that the trailing edgeof the sample is approximately ¼″ from the cardboard edge. The leadingedge of the sample is taped to the cardboard and table top such that theopposite (trailing) edge of the cardboard is positioned at the edge ofthe table top.

There will now be 3 first surface “out” samples on cardboard and(optionally) 3 second surface “out” samples on cardboard.

ii. Felt Preparation

Obtain a 30″×40″ piece of Crescent #300 cardboard from Cordage Inc. (800E. Ross Road, Cincinnati, Ohio, 45217). Using a paper cutter, cut outsix pieces of cardboard of dimensions of 2.25″×7.25″. Draw two linesparallel to the short dimension and down 1.125″ from the top and bottommost edges on the white side of the cardboard. Carefully score thelength of the line with a razor blade using a straight edge as a guide.Score it to a depth about half way through the thickness of the sheet.This scoring allows the felt/cardboard combination to fit tightly aroundthe weight of the Sutherland Rub tester. Draw an arrow running parallelto the long dimension of the cardboard on this scored side of thecardboard.

Cut six pieces of a black felt (F-55 or equivalent from New EnglandGasket, 550 Broad Street, Bristol, Conn. 06010) to the dimensions of2.25″×8.5″×0.0625″. Place the felt on top of the unscored, green side ofthe cardboard such that the long edges of both the felt and cardboardare parallel and in alignment. Also allow about 0.5″ of the black feltto overhang the top and bottom most edges of the cardboard. Snugly foldover both overhanging felt edges onto the backside of the cardboard withScotch brand tape, alternatively, the felt can be snugly fit to thecardboard when attaching the felt/cardboard combination to the weight,discussed below. Prepare a total of six of these felt/cardboardcombinations.

For the wet lint/pilling test, the felt/cardboard combination includes a9″ strip of Scotch brand tape (0.75″ wide) that is placed along eachedge of the felt (parallel to the long side of the felt) on the feltside that will be contacting the sample. The untapped felt between thetwo tape strips has a width between 18-21 mm. Three marks are placed onone of the strips of tape at 0, 4 and 8 centimeters from the trailingback edge of the felt.

All samples must be run with the same lot of felt.

iii. Felt/Cardboard/Weight Component

The felt/cardboard combination is associated with a weight. The weightmay include a clamping device to attach the felt/cardboard combinationto the weight. The weight and any clamping device totals five (5)pounds. The weight is available from Danilee Company, San Antonio, Tex.The weight has an effective contact area of 25.81 cm² (4 in²) andprovides a contact pressure of about 1.25 psi.

iv. Conducting Dry Lint/Pills Test

The amount of dry lint and/or dry pills generated from a fibrous productaccording to the present invention is determined with a Sutherland RubTester (available from Danilee Company, San Antonio, Tex.). This testeruses a motor to rub a felt/cardboard/weight component 5 times (back andforth) over the fibrous product, while the fibrous product is restrainedin a stationary position. The gray value of the felt is measured beforeand after the rub test. The difference between these two gray values isthen used to calculate a dry lint score and/or a dry pill score.

The Sutherland Rub Tester must first be calibrated prior to use. First,turn on the Sutherland Rub Tester pressing the “reset” button. Set thetester to run 5 strokes at the lower of the two speeds. One stroke is asingle and complete forward and reverse motion of the weight. The end ofthe rubbing block should be in the position closest to the operator atthe beginning and at the end of each test.

Prepare a calibration sample on cardboard as described above. Inaddition, prepare a calibration felt on cardboard as described above.Both of these calibration articles will be used for calibration of theinstrument and will not be used in the acquisition of data for theactual samples.

Place the calibration sample/cardboard combination on the base plate ofthe tester by slipping the holes in the board over the hold-down pins.The hold-down pins prevent the sample from moving during the test. Clipthe calibration felt/cardboard combination onto the weight componentdescribed above with the cardboard side contacting the pads of theweight. Make sure the calibration felt/cardboard combination is restingflat against the weight. Hook this weight onto the tester arm of theSutherland Rub Tester gently placing it on top of the calibrationsample/cardboard combination. The calibration felt must rest level onthe calibration sample and must be in 100% contact with the calibrationsample surface. Activate the Sutherland Rub Tester by pressing the“start” button.

Keep a count of the number of strokes and observe and make a mental noteof the starting and stopping position of the calibration felt coveredweight in relationship to the calibration sample. If the total number ofstrokes is five and if the position of the calibration felt coveredweight is the same at the end as it was in the beginning of the test,the tester is calibrated and ready to use. If the total number ofstrokes is not five or if the start and end positions of the calibrationfelt covered weight are different, then instrument may require servicingand/or recalibration. During the actual testing of samples, monitor andobserve the stroke count and the starting and ending points of the feltcovered weight.

v. Conducting Wet Lint/Pills Test

Wet lint/pills are determined by pulling, during one pass, a wettedfelt/cardboard/weight component over a sample.

To wet the felt, pipet 0.6 ml of deionized water onto the felt,distributing the water as evenly as possible between the 4 and 8 cmmarks as represented on the tape attached to the felt. Wait 10 secondsand then place the felt/cardboard/weight component on the center of thesample. After 1 second, pull the felt/cardboard/weight component by theleading edge horizontally until the felt/cardboard/weight component iscompletely off the table. Pull the weight in a manner to avoid placingany additional force on the felt/cardboard/weight component other thanthe horizontal pull force. The process of pulling thefelt/cardboard/weight component takes about 0.5 to 1.5 seconds. Thepulling process should occur as a substantially continuous or continuousmotion.

Carefully remove the felt/cardboard combination from thefelt/cardboard/weight component and allow to dry before capturing theimage. Then complete image analysis operations and calculations on thefelt and/or sample as described below.

vi. Image Capture

The images of the felt (untested), sample (untested) and felt (tested)are captured using a Nikon Digital Camera (DIX) with a Nikon Nikkor24-85 mm f2.8-f4 D 1F AF lens (set to 85 mm maximum zoom) and NikonCapture software installed on an appropriate computer. As schematicallyillustrated in FIG. 2, the camera 22 attached to a Kodak camerastand/lighting set-up (not shown) having four incandescent lamps 24(Polaroid MP-4 Land Camera model 44-22, 120 volt 150 watts each) thatare directed at the felt 26 positioned 31 cm (12.2 inches) under thelens of the mounted camera. The individual incandescent lamps 24 arepositioned 27.94 cm (11 inches) apart. Each pair of incandescent lamps24 are positioned 88.9 cm (35 inches) apart. The incandescent lamps 24are positioned 56.83 cm (22⅜ inches) above the felt 26. The camera isconnected via an appropriate cable to the computer. The camera should beturned on in PC mode. Turn the button to macro on the camera lens andflip the switch to the orange mark on the lens base. Adjust zoom to itsmaximum level of 85 mm. Turn the auto focus feature off. The NikonCapture software needs to be in operating order to capture images. Thesettings for the Nikon Capture software are as follows: Exposure1—manual exposure mode, 1/30 second shutter speed, f/6.3 aperture and0EV exposure compensation; Exposure 2—center weighted meter mode, ISO125 sensitivity and incandescent white balance; Storage Settings—raw (12bit) data format, no compression, color image type and large (3008×1960)image size; Mechanical—single shooting mode, single area AF area mode,manual focus mode. A calibration felt/cardboard combination is placedunder the camera such that the felt is centered under the lens of thecamera. Manually focus the camera on the felt. Take an image. Theexposure difference needs to be in the range of +2.5 to +2.75. Save theimage as a TIFF file (RGB) 8-bit. This image is used to perform the lintand pilling calculations in the Image Analysis Software (Optimas 6.5).Additional images of the sample/cardboard combination (untested) and thefelt/cardboard combination (tested) need to be captured in the samemanner. Also, an image of a known length standard (e.g., a ruler) istaken (exposure difference does not matter for this image).

vii. Image Analysis

The images captured are analyzed using Optimas 6.5 Image Analysissoftware commercially available from Media Cybernetics, L.P. Imagingset-up parameters, as listed herein, must be strictly adhered to inorder to have meaningfully comparative lint score and pill scoreresults.

First, an image with a known length standard (e.g., a ruler) is broughtup in Optimas, and used to calibrate length units (millimeters in thiscase).

For dry testing, the tested felt image has a region of interest (ROIarea) of approximately 4510 mm² (82 mm by 55 mm). The exact ROI area ismeasured and recorded (variable name: ROI area).

For wet lint/pills testing, the tested felt image has 2 regions ofinterest (ROI areas):

1) the “wetted” region (between the 4-8 cm marks on the tape) and 2) the“dragged” region (between the 0-4 cm marks on the tape). Each ROI areais approximately 608 mm² (38 mm×16 mm). The exact ROI area is measuredand recorded (variable name: ROI area).

An image of an untested black felt is opened, and the average gray value(using the same ROI of the untested felt as the tested felt) is measuredand recorded (variable name: untested felt Gray Value avg).

The tested sample luminance is saturated white (gray value=255) andconstant for samples of interest. If believed to be different, measurethe tested sample in a similar fashion as was done for the untestedfelt, and record (variable name: untested sample Gray Value avg).

The luminance threshold is calculated as the numerical average of theuntested felt Gray Value avg and untested sample Gray Value avg.

The tested felt image is opened, and the ROI is created and properlypositioned such that the ROI surrounds the region of the tested feltimage to be analyzed. The average luminance for the ROI is recorded(variable name: ROI Gray Value avg).

Pills are determined as follows: Optimas creates boundary lines in theimage where pixel luminance values cross through the threshold value(e.g., if the threshold a Gray Value of 155, boundary lines are createdwhere pixels of higher and lower value exist on either side. Thecriteria for determining a pill is that it must have an averageluminance greater than the threshold value, and have a perimeter lengthgreater than 2 mm for dry pills, and 0.5 mm for wet pills. The pillareas present in the ROI are summed (variable name: Total Pilled Area).

viii. Calculations

The data obtained from the image analysis is used in the followingcalculations:Pilled Area %=Total Pilled Area/ROI areaAvg. Pill Size(Area Weighted Avg.,mm²)=Σ(Pilled Areas)²/Total PilledAreaLint Score=unpilled felt Gray Value avg−untested felt Gray Value avg

where: unpilled felt Gray Value avg=[(ROI Gray Value avg*ROIarea)−(pilled Gray Value avg*pilled area)]/Total Unpilled AreaTotal Area Lint & Pill Score=ROI Gray Value avg−untested felt Gray Valueavg

By taking the average of the lint score on the first-side surface andthe second-side surface, the lint is obtained which is applicable tothat particular web or product. In other words, to calculate lint score,the following formula is used:

${{Dry}\mspace{14mu}{Lint}\mspace{14mu}{Score}} = \frac{\begin{matrix}{{{Dry}\mspace{14mu}{Lint}\mspace{14mu}{Score}},{{1^{st}\mspace{14mu}{side}} +}} \\{{{Dry}\mspace{14mu}{Lint}\mspace{14mu}{Score}},{2^{nd}\mspace{14mu}{side}}}\end{matrix}}{2}$${{Dry}\mspace{14mu}{Pill}\mspace{14mu}{Area}\mspace{14mu}\%} = \frac{\begin{matrix}{{{Dry}\mspace{14mu}{Pill}\mspace{14mu}{Area}\mspace{14mu}\%},{{1^{st}\mspace{14mu}{side}} +}} \\{{{Dry}\mspace{14mu}{Pill}\mspace{14mu}{Area}\mspace{14mu}\%},{2^{nd}\mspace{14mu}{side}}}\end{matrix}}{2}$${{Wet}\mspace{14mu}{Lint}\mspace{14mu}{Score}} = \frac{\begin{matrix}\begin{matrix}\begin{matrix}\lbrack ( {{{Wetted}\mspace{14mu}{Area}\mspace{14mu}{Lint}\mspace{14mu}{Score}} +}   \\{{ {{Dragged}\mspace{14mu}{Area}\mspace{14mu}{Lint}\mspace{14mu}{Score}} )\mspace{14mu} 1^{st}\mspace{14mu}{side}} +}\end{matrix} \\( {{{Wetted}\mspace{14mu}{Area}\mspace{14mu}{Lint}\mspace{14mu}{Score}} +} \end{matrix} \\ { {{Dragged}\mspace{14mu}{Area}\mspace{14mu}{Lint}\mspace{14mu}{Score}} )\mspace{14mu} 2^{nd}\mspace{14mu}{side}} \rbrack\end{matrix}}{2}$${{Wet}\mspace{14mu}{Pill}\mspace{14mu}{Area}\mspace{14mu}\%} = \frac{\begin{matrix}\begin{matrix}\begin{matrix}\lbrack ( {{{Wetted}\mspace{14mu}{Area}\mspace{14mu}{Pill}\mspace{20mu}{Area}{\mspace{14mu}\;}\%} +}   \\{{ {{Dragged}\mspace{14mu}{Area}{\mspace{11mu}\;}{Pill}\mspace{14mu}{Area}\mspace{14mu}\%} )\mspace{14mu} 1^{st}\mspace{14mu}{side}} +}\end{matrix} \\( {{{Wetted}\mspace{14mu}{Area}\mspace{14mu}{Pill}\mspace{14mu}{Area}\mspace{14mu}\%}\mspace{14mu} +} \end{matrix} \\ { {{Dragged}\mspace{14mu}{Area}\mspace{11mu}{Pill}\mspace{14mu}{Area}\mspace{14mu}\%} )\mspace{14mu} 2^{nd}\mspace{14mu}{side}} \rbrack\end{matrix}}{2}$

The fibrous structure and/or fibrous product of the present inventionmay exhibit a wet lint score of less than about 25 and/or a wet pillarea of less than about 4% and/or a dry lint score of less than about 50and/or a dry lint pill area of less than about 5%.

B. Shear Viscosity of a Polymer Melt Composition Measurement Test Method

The shear viscosity of a polymer melt composition of the presentinvention is measured using a capillary rheometer, Goettfert Rheograph6000, manufactured by Goettfert USA of Rock Hill S.C., USA. Themeasurements are conducted using a capillary die having a diameter D of1.0 mm and a length L of 30 mm (i.e., L/D=30). The die is attached tothe lower end of the rheometer's 20 mm barrel, which is held at a dietest temperature of 75° C. A preheated to die test temperature, 60 gsample of the polymer melt composition is loaded into the barrel sectionof the rheometer. Rid the sample of any entrapped air. Push the samplefrom the barrel through the capillary die at a set of chosen rates1,000-10,000 seconds⁻¹. An apparent shear viscosity can be calculatedwith the rheometer's software from the pressure drop the sampleexperiences as it goes from the barrel through the capillary die and theflow rate of the sample through the capillary die. The log (apparentshear viscosity) can be plotted against log (shear rate) and the plotcan be fitted by the power law, according to the formula η=Kγ^(n-1),wherein K is the material's viscosity constant, n is the material'sthinning index and γ is the shear rate. The reported apparent shearviscosity of the composition herein is calculated from an interpolationto a shear rate of 3,000 sec⁻¹ using the power law relation.

C. Shear Viscosity Change Test Method

Viscosities of three samples of a single polymer melt composition of thepresent invention comprising a crosslinking system to be tested aremeasured by filling three separate 60 cc syringes; the shear viscosityof one sample is measured immediately (initial shear viscosity) (ittakes about 10 minutes from the time the sample is placed in therheometer to get the first reading) according to the Shear Viscosity ofa Polymer Melt Composition Measurement Test Method. If the initial shearviscosity of the first sample is not within the range of 5-8Pascal-Seconds as measured at a shear rate of 3,000 sec⁻¹, then thesingle polymer melt composition has to be adjusted such that the singlepolymer melt composition's initial shear viscosity is within the rangeof 5-8 Pascal·Seconds as measured at a shear rate of 3,000 sec⁻¹ andthis Shear Viscosity Change Test Method is then repeated. Once theinitial shear viscosity of the polymer melt composition is within therange of 5-8 Pascal·Seconds as measured at a shear rate of 3,000 sec−1,then the other two samples are measured by the same test method afterbeing stored in a convection oven at 80° C. for 70 and 130 minutes,respectively. The shear viscosity at 3000 sec⁻¹ for the 70 and 130minute samples is divided by the initial shear viscosity to obtain anormalized shear viscosity change for the 70 and 130 minute samples. Ifthe normalized shear viscosity change is 1.3 times or greater after 70minutes and/or is 2 times or greater after 130 minutes, then thecrosslinking system within the polymer melt composition is unacceptable,and thus is not within the scope of the present invention. However, ifthe normalized shear viscosity change is less than 1.3 times after 70minutes and/or (preferably and) is less than 2 times after 130 minutes,then the crosslinking system is not unacceptable, and thus it is withinthe scope of the present invention with respect to polymer meltcompositions comprising the crosslinking system. Preferably, thecrosslinking system is acceptable with respect to polymeric structuresderived from polymer melt compositions comprising the crosslinkingsystem as determined by the Initial Total Wet Tensile Test Method.

Preferably, the normalized shear viscosity changes will be less than 1.2times after 70 minutes and/or less than 1.7 times after 130 minutes;more preferably less than 1.1 times after 70 minutes and/or less than1.4 times after 130 minutes.

D. Initial Total Wet Tensile Test Method

An electronic tensile tester (Thwing-Albert EJA Materials Tester,Thwing-Albert Instrument Co., 10960 Dutton Rd., Philadelphia, Pa.,19154) is used and operated at a crosshead speed of 4.0 inch (about10.16 cm) per minute and a gauge length of 1.0 inch (about 2.54 cm),using a strip of a polymeric structure of 1 inch wide and a lengthgreater than 3 inches long. The two ends of the strip are placed in theupper jaws of the machine, and the center of the strip is placed arounda stainless steel peg (0.5 cm in diameter). After verifying that thestrip is bent evenly around the steel peg, the strip is soaked indistilled water at about 20° C. for a soak time of 5 seconds beforeinitiating cross-head movement. The initial result of the test is anarray of data in the form load (grams force) versus crossheaddisplacement (centimeters from starting point).

The sample is tested in two orientations, referred to here as MD(machine direction, i.e., in the same direction as the continuouslywound reel and forming fabric) and CD (cross-machine direction, i.e.,90° from MD). The MD and CD wet tensile strengths are determined usingthe above equipment and calculations in the following manner:Initial Total Wet Tensile=ITWT(g _(f)/inch)=Peak Load_(MD)(g_(f))/2(inch_(width))+Peak Load_(CD)(g _(f))/2(inch_(width))

The Initial Total Wet Tensile value is then normalized for the basisweight of the strip from which it was tested. The normalized basisweight used is 36 g/m², and is calculated as follows:Normalized{ITWT}={ITWT}*36 (g/m²)/Basis Weight of Strip (g/m²)

If the initial total wet tensile of a polymeric structure, especially afibrous structure and/or fibrous product comprising a polymericstructure comprising a crosslinking system of the present invention isat least 3 g/2.54 cm (3 g/in) and/or at least 4 g/2.54 cm (4 g/in)and/or at least 5 g/2.54 cm (5 g/in), then the crosslinking system isacceptable and is, along with its corresponding polymeric structureand/or fibrous structure and/or fibrous product, within the scope of thepresent invention.

E. Fiber Diameter Test Method

A polymeric structure comprising fibers of appropriate basis weight(approximately 5 to 20 grams/square meter) is cut into a rectangularshape, approximately 20 mm by 35 mm. The sample is then coated using aSEM sputter coater (EMS Inc, PA, USA) with gold so as to make the fibersrelatively opaque. Typical coating thickness is between 50 and 250 nm.The sample is then mounted between two standard microscope slides andcompressed together using small binder clips. The sample is imaged usinga 10× objective on an Olympus BHS microscope with the microscopelight-collimating lens moved as far from the objective lens as possible.Images are captured using a Nikon D1 digital camera. A Glass microscopemicrometer is used to calibrate the spatial distances of the images. Theapproximate resolution of the images is 1 μm/pixel. Images willtypically show a distinct bimodal distribution in the intensityhistogram corresponding to the fibers and the background. Cameraadjustments or different basis weights are used to achieve an acceptablebimodal distribution. Typically 10 images per sample are taken and theimage analysis results averaged.

The images are analyzed in a similar manner to that described by B.Pourdeyhimi, R. and R. Dent in “Measuring fiber diameter distribution innonwovens” (Textile Res. J. 69(4) 233-236, 1999). Digital images areanalyzed by computer using the MATLAB (Version. 6.3) and the MATLABImage Processing Tool Box (Version 3.) The image is first converted intoa grayscale. The image is then binarized into black and white pixelsusing a threshold value that minimizes the intraclass variance of thethresholded black and white pixels. Once the image has been binarized,the image is skeltonized to locate the center of each fiber in theimage. The distance transform of the binarized image is also computed.The scalar product of the skeltonized image and the distance mapprovides an image whose pixel intensity is either zero or the radius ofthe fiber at that location. Pixels within one radius of the junctionbetween two overlapping fibers are not counted if the distance theyrepresent is smaller than the radius of the junction. The remainingpixels are then used to compute a length-weighted histogram of fiberdiameters contained in the image.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be considered as an admission that it is prior artwith respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A method for making a fibrous structure, the method comprising thesteps of: a. providing a polymer melt composition comprising a non-PVOHhydroxyl polymer starch and a crosslinking agent comprising animidazolidinone; b. polymer processing the polymer melt composition suchthat the imidazolidinone crosslinks the non-PVOH hydroxyl polymer starchto form a plurality of fibers; c. collecting the plurality of fibers toform a fibrous structure; d. curing the fibers; and e. fusing two ormore fibers together at one or more positions along the fiber lengthssuch that at the point of fusing one fiber unit is formed.
 2. The methodaccording to claim 1 wherein the method further comprises the step ofdifferentially densifying the fibrous structure such that two or moreregions exhibit different densities relative to each other.
 3. Themethod according to claim 2 wherein the step of differentiallydensifying comprises contacting the fibrous structure with astructure-imparting element comprising a pattern in the presence ofhumidity such that the fibrous structure takes the shape of the patternon the structure-imparting element.
 4. The method according to claim 2wherein the step of differentially densifying the fibrous structurecomprises sandwiching the fibrous structure between two belts in thepresence of humidity, wherein at least one of the belts is a structuredbelt comprising a pattern such that the fibrous structure takes theshape of the pattern on the structured belt.
 5. The method according toclaim 1 wherein the polymer processing step comprises dry spinning thepolymer melt composition.
 6. The method according to claim 1 wherein themethod further comprises the step of adding cellulose fibers incombination with the plurality of fibers to make the fibrous structure.